There are still patent issues with MP3. IIRC for about 1 or 2 more years. That means its "LGPL" with extra lawyer sauce. Much like H264, mpeg2 and there kin, its not clear even in the EU if patents on software can't be enforced . The advice given to me was while you don't make money, you won't have a problem. If you sell it for cash, I don't want to be your lawyer anymore (this was with regard to the EU market place).

In the US its very clear. You need a license.

I have no special talents. I am only passionately curious.--Albert Einstein

You might be able to get around licensing issues (if you are worried about that) by using qtjava, QuickTime for Java. It requires users to install QT (and check a box to also install the qtjava bit) and then you can make use of QT from Java, which supports many formats. I think this way Apple pays the MP3 licensing fees and you are in teh clear. If you find most users don't install the qtjava portion when installing QT, it is a pain for them to reinstall QT just for your app to work. In this case you can distribute the qtjava JAR along with your app, though this probably goes against Apple's usage agreements for qtjava.

BTW, qtjava will eventually not be supported by Apple. It still works on Snow Leopard though.

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